1. Field of the Invention
This invention relates to an intake muffler, which is particularly intended for use in two-stroke-cycle internal combustion engines and comprises a stiff housing, in which a partition defines two chambers, which communicate with each other through at least two tubes, which extend through the partition, wherein the first chamber has a larger volume than the second and is provided with an inlet tube and contains an air filter insert and the second chamber communicates with a tubular outlet port.
2. Description of the Prior Art
A muffler of that kind, which is known from practice, comprises a cylindrical, non-partitioned inlet tube and in most cases there is only a single communicating tube. If there are two or more of such communicating tubes, they are equal in diameter and in length and the muffler is flown through only in one direction.
A disadvantage of that known muffler resides in that there is a high pressure drop in relation to the tube length, which results in desirable acoustic properties, and in relation to the tube diameter, which is also favorable from an acoustic aspect. That high pressure drop will obviously reduce the power of the engine. The presence of the single communicating tube or of a plurality of communicating tubes which are equal in length involve a risk of an occurrence of pronounced natural frequencies, which will give rise to unpleasant noise and to a higher sound level. Because the muffler is flown through only in one direction, there is only a poor damping of sound owing to a lack of appropriate reflections.
From Austrian Patent Specification 235,089 it is also known to connect the several chambers of a sound-damping filter by means of tubes which differ in length and in diameter. But that known muffler is of an entirely different design and comprises a pure air chamber, an adjacent secondary damping chamber, an intermediate damping chamber, and a primary damping chamber. The pure air tube leads from the pure air chamber directly to the outlet and has only slots in the intermediate chamber and in the primary damping chamber and a relatively short tube which is smaller in diameter extends from the pure air chamber only into the secondary damping chamber, which has no outlet opening. That known muffler constitutes a relatively intricate sheet metal structure, which results in entirely different conditions.